Modern Mind: An Intellectual History of the 20th Century (25 page)

Though Bingham returned in 1912 and 1915 to make further surveys and
discoveries, it was Machu Picchu that claimed the world’s attention. The city that emerged from the careful excavations had a beauty that was all its own.
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This was partly because so many of the buildings were constructed from interlocking Inca masonry, and partly because the town was remarkably well preserved, intact to the roofline. Then there was the fact of the city’s unity – house groups surrounded by tidy agricultural terraces, and an integrated network of paths and stairways, hundreds of them. This made it easy for everyday life in Inca times to be imagined. The location of Machu Picchu was also extraordinary: after the jungle had been cleared, the remoteness on a narrow ridge surrounded by a hairpin canyon many feet below was even more apparent. An exquisite civilisation had been isolated in a savage jungle.
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Bingham was convinced that Machu Picchu was Vilcabamba. One reason he thought this was because he had discovered, beyond the city, no fewer than 135 skeletons, most of them female and many with skulls that had been trepanned, though none in the town itself. Bingham deduced that the trepanned skulls belonged to foreign warriors who had not been allowed inside what was clearly a holy city. (Not everyone agrees with this interpretation.) A second exciting and strange discovery added to this picture: a hollow tube was found which Bingham believed had been used for inhalation. He thought the tube had probably formed part of an elaborate religious ceremony and that the substance inhaled was probably a narcotic such as the yellow seed of the local huilca tree. By extension, therefore, this one tube could be used to explain the name Vilcabamba: plain (bamba) of Huilca. Bingham’s final argument for identifying the site as Vilcabamba was based on the sheer size of Machu Picchu. Its roughly one hundred houses made it the most important ruin in the area, and ancient Spanish sources had described Vilcabamba as the largest city in the province – therefore it seemed only common sensical that when Manco Inca sought refuge from Pizarro’s cavalry he would have fallen back to this well-defended place.
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These arguments seemed incontrovertible. Machu Picchu was duly identified as Vilcabamba, and for half a century the majority of archaeological and historical scholars accepted that the city was indeed the last refuge of Manco Inca, the site of his wife’s terrible torture and death.
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Bingham was later proved wrong. But at the time, his discoveries, like Boas’s and Morgan’s, acted as a careful corrective to the excesses of the race biologists who were determined to jump to the conclusion that, following Darwin, the races of the world could be grouped together on a simple evolutionary tree. The very strangeness of the Incas, the brilliance of their art and buildings, the fantastic achievement of their road network, stretching over 19,000 miles and superior in some ways to the European roads of the same period, showed the flaws in the glib certainties of race biology. For those willing to listen to the evidence in various fields, evolution was a much more complex process than the social Darwinists allowed.

There was no denying the fact that the idea of evolution was growing more popular, however, or that the work of Du Bois, Morgan, Boas, and Bingham did hang together in a general way, providing new evidence for the links
between animals and man, and between various racial groups across the world. The fact that social Darwinism was itself so popular showed how powerful the idea of evolution was. Moreover, in 1914 it received a massive boost from an entirely new direction. Geology was beginning to offer a startling new understanding of how the world itself had evolved.

Alfred Wegener
was a German meteorologist. His
Die Entstehung der Kontinente und Ozeane
(The Origin of Continents and Oceans) was not particularly original. His idea in the book that the six continents of the world had begun life as one supercontinent had been aired earlier by an American, F. B. Taylor, in 1908. But Wegener collected much more evidence, and more impressive evidence, to support this claim than anyone else had done before. He set out his ideas at a meeting of the German Geological Association at Frankfurt-am-Main in January 1912.
⁵⁵
In fact, with the benefit of hindsight one might ask why scientists had not reached Wegener’s conclusion sooner. By the end of the nineteenth century it was obvious that to make sense of the natural world, and its distribution around the globe, some sort of intellectual explanation was needed. The evidence of that distribution consisted mostly of fossils and the peculiar spread of related types of rocks. Darwin’s
On the Origin of Species
had stimulated an interest in fossils because it was realised that if they could be dated, they could throw light on the development of life in bygone epochs and maybe even on the origin of life itself. At the same time, quite a lot was known about rocks and the way one type had separated from another as the earth had formed, condensing from a mass of gas to a liquid to a solid. The central problem lay in the spread of some types of rocks across the globe and their links to fossils. For example, there is a mountain range that runs from Norway to north Britain and that should cross in Ireland with other ridges that run through north Germany and southern Britain. In fact, it looked to Wegener as though the crossover actually occurs near the coast of north America, as if the two seaboards of the north Atlantic were once contiguous.
⁵⁶
Similarly, plant and animal fossils are spread about the earth in a way that can only be explained if there were once land connections between areas that are now widely separated by vast oceans.
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The phrase used by nineteenth-century scientists was ‘land bridges,’ convenient devices that were believed to stretch across the waters to link, for example, Africa to South America, or Europe to North America. But if these land bridges had never existed, where had they gone to? What had provided the energy by which the bridges had arisen and disappeared? What happened to the seawaters?

Wegener’s answer was bold. There were no land bridges, he said. Instead, the six continents as they now exist – Africa, Australia, North and South America, Eurasia, and Antarctica – were once one huge continent, one enormous land mass which he called
Pangaea
(from the Greek for
all
and
earth).
The continents had arrived at their present positions by ‘drifting,’ in effect floating like huge icebergs. His theory also explained midcontinent mountain ridges, formed by ancient colliding land masses.
⁵⁸
It was an idea that took some getting used to. How could entire continents ‘float’? And on what? And if the continents had moved, what enormous force had moved them? By Wegener’s
time the earth’s essential structure was known. Geologists had used analysis of earthquake waves to deduce that the earth consisted of a crust, a mantle, an outer core, and an inner core. The first basic discovery was that all the continents of the earth are made of one form of rock, granite - or a granular igneous rock (formed under intense heat) – made up of feldspar and quartz. Around the granite continents may be found a different form of rock - basalt, much denser and harder. Basalt exists in two forms, solid and molten (we know this because lava from volcanic eruptions is semi-molten basalt). This suggests that the relation between the outer structures and the inner structures of the earth was clearly related to how the planet formed as a cooling mass of gas that became liquid and then solid.

The huge granite blocks that form the continents are believed to be about 50 kilometres (30 miles) thick, but below that, for about 3,000 kilometres (1,900 miles), the earth possesses the properties of an ‘elastic solid,’ or semi-molten basalt. And below that, to the centre of the earth (the radius of which is about 6,000 kilometres – nearly 4,000 miles), there is liquid iron.
*
Millions of years ago, of course, when the earth was much hotter than it is today, the basalt would have been less solid, and the overall situation of the continents would have resembled more closely the idea of icebergs floating in the oceans. On this view, the drifting of the continents becomes much more conceivable.

Wegener’s theory was tested when he and others began to work out how the actual land masses would have been pieced together. The continents do not of course consist only of the land that we see above sea level at the present time. Sea levels have risen and fallen throughout geological time, as ice ages have lowered the water table and warmer times raised them, so that the continental shelves - those areas of land currently below water but relatively shallow, before the contours fall off sharply by thousands of feet - are just as likely to make the ‘fit.’ Various unusual geological features fall into place when this massive jigsaw is pieced together. For example, deposits from glaciation of permocarboniferous age (i.e., ancient forests, which were formed 200 million years ago and are now coalfields) exist in identical forms on the west coast of South Africa and the east coast of Argentina and Uruguay. Areas of similar Jurassic and Cretaceous rocks (roughly 100—200 million years old) exist around Niger in West Africa and around Recife in Brazil, exactly opposite, across the South Atlantic. And a geosyncline (a depression in the earth’s surface) that extends across southern Africa also strikes through mid-Argentina, aligning neatly. Finally, there is the distribution of the distinctive Glossopteris flora, similar fossils of which exist in both South Africa and other faraway southern continents, like South America and Antarctica. Wind is unlikely to account for this dispersal, since the seeds of Glossopteris were far too bulky to have been spread
in that way. Here too, only continental drift can account for the existence of this plant in widely separated places.

How long was Pangaea in existence, and when and why did the breakup occur? What kept it going? These are the final questions in what is surely one of the most breathtaking ideas of the century. (It took some time to catch on: in 1939, geology textbooks were still treating continental drift as ‘a hypothesis only.’ Also see chapter 31, below.)
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The theory of continental drift coincided with the other major advance made in geology in the early years of the century. This related to the age of the earth. In 1650, James Ussher, archbishop of Armagh in Ireland, using the genealogies given in the Bible, had calculated that the earth was created at 9:00
A.M.
on 26 October 4004
B.C.
*
It became clear in the following centuries, using fossil evidence, that the earth must be at least 300 million years old; later it was put at 500 million. In the late nineteenth century William Thomson, Lord Kelvin (1824–1907), using ideas about the earth’s cooling, proposed that the crust formed between 20 million and 98 million years ago. All such calculations were overtaken by the discovery of radioactivity and radioactive decay. In 1907 Bertram Boltwood realised that he could calculate the age of rocks by measuring the relative constituents of uranium and lead, which is the final decay product, and relating it to the half-life of uranium. The oldest substances on earth, to date, are some zircon crystals from Australia dated in 1983 to 4.2 billion years old; the current best estimate of the age of the earth is 4.5 billion years.
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The age of the oceans has also been calculated. Geologists have taken as their starting point the assumption that the world’s oceans initially consisted entirely of fresh water, but gradually accumulated salts washed off the continents by the world’s rivers. By calculating how much salt is deposited in the oceans each year, and dividing that into the overall salinity of the world’s body of seawater, a figure for the time such salination has taken can be deduced. The best answer at the moment is between 100 and 200 million years.
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In trying to set biology to one side in his understanding of the Negro position in the United States, Du Bois grasped immediately what some people took decades to learn: that change for the Negro could only come through political action that would earn for a black skin the same privileges as a white one. He nevertheless underestimated (and he was not alone) the ways in which different forms of knowledge would throw up results that, if not actually haphazard, were not entirely linear either, and which from the start began to flesh out Darwin’s theory of evolution. Throughout the twentieth century, the idea of evolution would have a scientific life and a popular life, and the two were not always identical. What people thought about evolution was as important as what evolution really was. This difference was especially important in the United States, with its unique ethnic/biological/social mix, a nation of immigrants
so different from almost every other country in the world. The role of genes in history, the brainpower of the different races, as evolved, would never go away as the decades passed.

The slow pace of evolution, operating over geological time, and typified by the new realisation of the great age of the earth, contributed to the idea that human nature, like fossils, was set in stone. The predominantly unvarying nature of genes added to that sense of continuity, and the discovery of sophisticated civilisations that had once been important but had collapsed encouraged the idea that earlier peoples, however colourful and inventive, had not become extinct without deserving to. And so, while physics undermined conventional notions of reality, the biological sciences, including archaeology, anthropology, and geology, all started to come together, even more so in the popular mind than in the speciahst scientific mind. The ideas of linear evolution and of racial differences went together. It was to prove a catastrophic conjunction.